How to implement timeout for getline()?

Question

I want to read a string from command line through getline() in c++.

For that I want to add a timer of 5 sec. If no string read, then the program will terminate.

How can I do this?

@RandyHoward : I don't think this is an exact duplicate. `getline()` is much simpler to use, and know how to add a counter to it would be useful to those who are new. This question should remain legitimate. — Games Brainiac, Mar 20 '13 at 13:00
@kassak : Nope, still not an exact duplicate, the answers show that, I think. Either way, I think this is a useful question, because `getline()` is used quite a lot, and knowing how to use it well would be good for future readers. Just my 2 cents. — Games Brainiac, Mar 20 '13 at 13:06
StackOverflow is not the proper place for this question. We do not write your code for you. You need to do your own coding and if you aren't sure why something is not working as expected, post the code with an explanation of what you were expecting it to do, and what it is actually doing including all error messages. See [about StackOverflow](http://stackoverflow.com/about). — Lightness Races in Orbit, Mar 20 '13 at 13:09
@LightnessRacesinOrbit I would say the question is ok (after edit), since it has [quite good answer](http://stackoverflow.com/a/15524177/476681) — BЈовић, Mar 20 '13 at 13:13
@GamesBrainiac no, this is not about using `getline` "well"; quite the opposite. If you need this kind of functionality, hacking it into getline is silly, because it will be a messy brittle hack. There are better ways of doing this, and they involve not using getline. — R. Martinho Fernandes, Mar 20 '13 at 13:21
many ways..?? good.. what are the ways you have to solve this problem ?? - R. Martinho Fernandes — Reddi Rajendra P, Mar 21 '13 at 05:43
@R.MartinhoFernandes : Why don't you elaborate on that, since you seem to know it quite well. — Games Brainiac, Mar 21 '13 at 08:49
There is no standard-based solution to this, but there are libraries that can be used to do it, like ncurses. — R. Martinho Fernandes, Mar 21 '13 at 09:49

score 8 · Answer 1 · answered Mar 20 '13 at 13:22

8

ok, wait for 5 sec, and terminate if there was no input:

#include <thread>
#include <atomic>
#include <iostream>
#include <string>

int main()
{
    std::atomic<bool> flag = false;
    std::thread([&]
    {
        std::this_thread::sleep_for(std::chrono::seconds(5));

        if (!flag)
            std::terminate();
    }).detach();

    std::string s;
    std::getline(std::cin, s);
    flag = true;
    std::cout << s << '\n';
}

answered Mar 20 '13 at 13:22

Abyx

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+1 for standard solution, hehe – R. Martinho Fernandes Mar 20 '13 at 13:24
with out using threads pllzzz... – Reddi Rajendra P Mar 20 '13 at 13:35
@user2164410 - why not - it's the usual way of handling such requirements. It would just as easy to allow the signaling of a line entry before the 5 seconds is up, rather than waiting until the end of the interval. – Martin James Mar 20 '13 at 13:48
1

-Martin James that's okay.. But, now what i want is.. if i am not reading any string after 5 sec i don't want to exit from program, i needs to call another function and come back to the getline(). (Looping). thanks – Reddi Rajendra P Mar 21 '13 at 05:17
-Abyx it is giving many compile time errors.. compile the code once .. and if possible don't include any threads. thanks – Reddi Rajendra P Mar 21 '13 at 05:32
I basically did this without the knowledge that the thread would continue taking input and got flamed for hoping it could work :p – chris Mar 21 '13 at 07:02

cnicutar · Accepted Answer · 2013-03-20T13:23:33.417

3

How about:

/* Wait 5 seconds. */
alarm(5);

/* getline */

/* Cancel alarm. */
alarm(0);

Alternatively you could use setitimer.

As R. Martinho Fernandes requested:

The function alarm arranges for the current process to receive a SIGALRM in 5 seconds from its call. The default action for a SIGALRM si to terminate the process abnormally. Calling alarm(0) disables the timer.

edited Mar 20 '13 at 13:23

answered Mar 20 '13 at 12:56

cnicutar

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I wonder if there's a way to close and reopen stdin or something to get past the getline statement...? – sje397 Mar 20 '13 at 13:01
and at last i m getting output as "Alarm clock". How to suppress that one ??? thanks @cnicutar – Reddi Rajendra P Mar 20 '13 at 13:05
1

If this answered your original question, it'll work better to accept this answer, and ask a new question about the "Alarm clock" output showing your code. – Useless Mar 20 '13 at 13:07
Can you explain why this works? – R. Martinho Fernandes Mar 20 '13 at 13:15
@R.MartinhoFernandes Good call, edited. – cnicutar Mar 20 '13 at 13:23
@cnicutar: I think it'd be good to add that `alarm` is POSIX-specific. – Mar 20 '13 at 13:24
Thanks for adding the explanation; have a +1. – R. Martinho Fernandes Mar 20 '13 at 13:25
with out using "alarm(0)" if i want to continue with some other task, then how to use..?? thanks .. -cnicutar – Reddi Rajendra P Mar 20 '13 at 13:33
@user2164410 I don't understand what you're asking – cnicutar Mar 20 '13 at 13:39
after 5 seconds alarm(0) is executing and the program terminating. But, now after 5 sec if i want to do some other task. then ?? -cnicutar – Reddi Rajendra P Mar 20 '13 at 13:41
2

`alarm(0)` should _disable_ the timer. – Useless Mar 20 '13 at 13:42

How to implement timeout for getline()?

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